In the European Union, emissions of nitrogen oxides (NOx), total hydrocarbon (THC), non-methane hydrocarbons (NMHC), carbon monoxide (CO) and particulate matter (PM) are regulated for most vehicle types, including cars, trucks (lorries), locomotives, tractors and similar machinery, barges, but excluding seagoing ships and aeroplanes. For each vehicle type, different standards apply. Compliance is determined by running the engine at a standardised test cycle. Non-compliant vehicles cannot be sold in the EU, but new standards do not apply to vehicles already on the roads. No use of specific technologies is mandated to meet the standards, though available technology is considered when setting the standards. New models introduced must meet current or planned standards, but minor lifecycle model revisions may continue to be offered with pre-compliant engines.

Along with Emissions standards the European Union has also mandated a number of computer on-board diagnostics for the purposes of increasing safety for drivers. These standards are used in relation to the emissions standards.

In the early 2000s, Australia began harmonising Australian Design Rule certification for new motor vehicle emissions with Euro categories. Euro III was introduced on 1 January 2006 and is progressively being introduced to align with European introduction dates.

The legal framework consists in a series of directives, each amendments to the 1970 Directive 70/220/EEC.[1] The following is a summary list of the standards, when they come into force, what they apply to, and which EU directives provide the definition of the standard.

Commission Directive 2001/116/EC of 20 December 2001, adapting to technical progress Council Directive 70/156/EEC on the approximation of the laws of the Member States relating to the type-approval of motor vehicles and their trailers[9][10]

Directive 2002/24/EC of the European Parliament and of the Council of 18 March 2002 relating to the type-approval of two or three-wheeled motor vehicles and repealing Council Directive 92/61/EEC

Emission standards for passenger cars and light commercial vehicles are summarised in the following tables. Since the Euro 2 stage, EU regulations introduce different emission limits for diesel and petrol vehicles. Diesels have more stringent CO standards but are allowed higher NOx emissions. Petrol-powered vehicles are exempted from particulate matter (PM) standards through to the Euro 4 stage, but vehicles with direct injection engines are subject to a limit of 0.0045 g/km for Euro 5 and Euro 6. A particulate number standard (P) or (PN) has been introduced in 2011 with Euro 5b for diesel engines and in 2014 with Euro 6 for petrol engines.[11][12][13]

From a technical perspective, European emissions standards do not reflect everyday usage of the vehicle as manufacturers are allowed to lighten the vehicle by removing the back seats, improve aerodynamics by taping over grilles and door handles or reduce the load on the generator by switching off the headlights, the passenger compartment fan or simply disconnecting the alternator which charges the battery.[14]

* Before Euro 5, passenger vehicles > 2500 kg were type approved as light commercial vehicles N1 Class I ** Applies only to vehicles with direct injection engines*** 6×1012/km within first three years from Euro 6b effective dates† Values in parentheses are conformity of production (COP) limits

The emission standards for vehicles for trucks (lorries) and buses are defined by engine energy output in g/kWh; this is unlike the emission standards for passenger cars and light commercial vehicles, which are defined by vehicle driving distance in g/km - a general comparison to passenger cars is therefore not possible, as the kWh/km factor depends (among other) on the specific vehicle.

The official category name is heavy-duty diesel engines, which generally includes lorries and buses.

The following table contains a summary of the emission standards and their implementation dates. Dates in the tables refer to new type approvals; the dates for all new registrations are in most cases one year later.

Enhanced environmentally friendly vehicle or EEV is a term used in the European emission standards for the definition of a "clean vehicle" > 3.5 tonne in the category M2 and M3. The standard lies between the levels of Euro V and Euro VI.

European standards for non-road diesel engines harmonize with the US EPA standards, and comprise gradually stringent tiers known as Stage I–V standards. The Stage I/II was part of the 1997 directive (Directive 97/68/EC). It was implemented in two stages with Stage I implemented in 1999 and Stage II implemented between 2001 and 2004. In 2004, the European Parliament adopted Stage III/IV standards. The Stage III standards were further divided into Stage III A and III B were phased in between 2006 and 2013. Stage IV standards are enforced from 2014. Stage V standards are phased-in from 2018 with full enforcement from 2021.

As of 1 January 2015, EU Member States have to ensure that ships in the Baltic, the North Sea and the English Channel are using fuels with a sulphur content of no more than 0.10%. Higher sulphur contents are still possible, but only if the appropriate exhaust cleaning systems are in place.[16]

Just as important as the regulations are the tests needed to ensure adherence to regulations. These are laid out in standardised emission test cycles used to measure emissions performance against the regulatory thresholds applicable to the tested vehicle.

Since the Euro 3 regulations in 2000, performance has been measured using the New European Driving Cycle test (NEDC; also known as MVEG-B), with a "cold start" procedure that eliminates the use of a 40-second engine warm-up period found in the ECE+EUDC test cycle (also known as MVEG-A).[12][17]

The two groups of emissions standards for heavy duty vehicles each have different appropriate test requirements. Steady-state testing is used for diesel engines only, while transient testing applies to both diesel and petrol engines.[18]

For the emission standards to deliver actual emission reductions it is crucial to use a test cycle that reflects real-world driving conditions. It was discovered[20] that vehicle manufacturers would optimise emissions performance only for the test cycle, whilst emissions from typical driving conditions proved to be much higher than when tested. Some manufacturers were also found to use so-called defeat devices where the engine control system would recognise that the vehicle was being tested, and would automatically switch to a mode optimised for emissions performance. The use of a defeat device is expressly forbidden in EU law.[13]

An independent study in 2014 used portable emissions measurement systems to measure NOx emissions during real world driving from fifteen Euro 6 compliant diesel passenger cars. The results showed that NOx emissions were on average about seven times higher than the Euro 6 limit. However, some of the vehicles did show reduced emissions, suggesting that real world NOx emission control is possible.[21] In one particular instance, research in diesel car emissions by two German technology institutes found that zero 'real' NOx reductions in public health risk had been achieved despite 13 years of stricter standards (2006 report).[22]

In 2015, the Volkswagen emissions scandal involved revelations that Volkswagen AG had deliberately falsified emission reports by programming engine management unit firmware to detect test conditions, and change emissions controls when under test. The cars thus passed the test, but in real world conditions, emitted up to forty times more NOx emissions than allowed by law.[23] An independent report in September 2015 warned that this extended to "every major car manufacturer",[24] with BMW, and Opel named alongside Volkswagen and its sister company Audi as "the worst culprits",[24] and that approximately 90% of diesel cars "breach emissions regulations".[24] Overlooking the direct responsibility of the companies involved, the authors blamed the violations on a number of factors, including "unrealistic test conditions, a lack of transparency and a number of loopholes in testing protocols".[24]

In 2017, the European Union will introduce testing in real-world conditions called Real Driving Emissions, using portable emissions measurement systems in addition to laboratory tests.[25] The actual limits will use 110% (CF=2.1) "conformity factor" (the difference between the laboratory test and real-world conditions) in 2017, and 50% (CF=1.5) in 2021 for NOx,[26] conformity factor for particles number P being left for further study. Environment organizations criticized the decision as insufficient,[27][28] while ACEA mentions it will be extremely difficult for automobile manufacturers to reach such a limit in such short period of time.[29] In 2015 an ADAC study (ordered by ICCT) of 32 Euro 6 cars showed that few complied with on-road emission limits, and LNT/NOx adsorber cars (with about half the market) had the highest emissions.[30] At the end of this study, ICCT was expecting a 100% conformity factor.[31]

NEDC Euro 6b not to exceed limit of 80 mg/km NOx will then continue to apply for the WLTC Euro 6c tests performed on a dynomometer while WLTC-RDE will be performed in the middle of the traffic with a PEMS attached at the rear of the car. RDE testing is then far more difficult than the dynomometer tests. RDE not to exceed limits have then been updated to take into account different test conditions such as PEMS weight (305–533 kg in various ICCT testing[32]), driving in the middle of the traffic, road gradient, etc.

ADAC also performed NOx emission tests with a cycle representative of the real driving environment in the laboratory.[33][34] Among the 69 cars tested:

17 cars emit less than 80 mg/km i-e do not emit more NOx on this more demanding cycle than on the NEDC cycle

22 additional cars fall below the 110% conformity factor. In total: 57% of cars have then a good chance to be compatible with WLTC-RDE

30 cars fall above the 110% conformity factor and have then to be improved to satisfy the WLTC-RDE test.

Since 2012, ADAC performs regular pollutant emission tests [35][36] on a specific cycle in the laboratory duly representing a real driving environment and gives a global notation independent from the type of engine used (petrol, diesel, natural gas, LPG, hybrid, etc.). To get the maximum 50/50 note on this cycle, the car shall emit less than the minimum limit applicable to either petrol or diesel car, that is to say 100 mg HC, 500 mg CO, 60 mg NOx, 3 mg PM and 6×1010 PN. Unlike ambient discourse dirty diesel versus clean petrol cars, the results are much more nuanced and subtle. Some Euro 6 diesel cars perform as well as the best hybrid petrol cars; some other recent Euro 6 petrol indirect injection cars perform as the worst Euro 5 diesel cars; finally some petrol hybrid cars are at the same level as the best Euro 5 diesel cars.[37][38]

Tests commissioned by Which? from the beginning of 2017 found that 47 out of 61 diesel car models exceed the Euro 6 limit for NOx, although they conform to official standards.[39]

Within the European Union, road transport is responsible for about 20% of all CO2 emissions, with passenger cars and vans contributing about 15%.[40][41][when?]

The target fixed at Kyoto Protocol was an 8% reduction of emissions in all sectors of the economy compared to 1990 levels by 2008–12.

Relative CO2 emissions from transport have risen rapidly in recent years, from 21% of the total in 1990 to 28% in 2004,[40][42][43] but currently there are no standards for limits on CO2 emissions from vehicles.

EU transport emissions of CO2 currently[when?] account for about 3.5% of total global CO2 emissions.

The purpose of Directive 1999/94/EC of the European Parliament and the Council of 13 December 1999 relating to the availability of consumer information on fuel economy and CO2 emissions in respect of the marketing of new passenger cars[44] is to ensure that information relating to the fuel economy and CO2 emissions of new passenger cars offered for sale or lease in the Community is made available to consumers in order to enable consumers to make an informed choice.

In the United Kingdom, the initial approach was deemed ineffective. The way the information was presented was too complicated for consumers to understand. As a result, car manufacturers in the United Kingdom voluntarily agreed to put a more “consumer-friendly,” colour-coded label displaying CO2 emissions on all new cars beginning in September 2005, with a letter from A (<100 CO2 g/km) to F (186+ CO2 g/km). The goal of the new “green label” is to give consumers clear information about the environmental performance of different vehicles.[45]

Other EU member countries are also in the process of introducing consumer-friendly labels.

EU Regulation No 443/2009 sets an average CO2 emissions target for new passenger cars of 130 grams per kilometre. The target is gradually being phased in between 2012 and 2015. A target of 95 grams per kilometre will apply from 2021.

For light commercial vehicle, an emissions target of 175 g/km applies from 2017, and 147 g/km from 2020.[46]

As Europe's requirements for its vehicle fleets head toward a goal of 98 grams of CO2 per kilometer by 2020, Christian Maloney of the German office of consulting group McKinsey & Co. says the only way the automakers can get there and make money is with plug-in vehicles.[47][48]

Many EU member states have responded to this problem by exploring the possibility of including electric vehicle-related infrastructure into their existing road traffic system, with some even having begun implementation. The UK has begun its "plugged-in-places" scheme which sees funding go to several areas across the UK in order to create a network of charging points for electric vehicles.[49]